As the level of hearing impairment may vary significantly with individual patients, the hearing aid device must be programmed for each individual case such that the patient is in particular able to listen to and understand even very quiet tone signals or noises. Very loud tone signals are however less significantly amplified, since they can be better perceived by the patient. There is also the problem of the signal-to-noise ratio being sufficiently high for an amplified tone signal to be output with the lowest possible noise level, in order herewith to achieve the best possible understanding. To solve this problem, in the case of known hearing aid devices, the sound pressure level emitted by the loudspeaker is controlled as a function of the sound pressure level recorded on the microphone. In such cases the transmitted frequency range is herewith divided into two or more amplification channels and is controlled separately by corresponding control loops. The division into sub regions is carried out by input-side filters, which are connected to their own dynamics controller.
DE 2641675 A1 discloses a hearing aid device having an audio frequency amplifier, which amplifies the audio signals recorded by a microphone and forwards them to a receiver. The audio frequency amplifier has at least two transmission channels which are connected in parallel. On the input side, each transmission channel contains a filter with a control amplifier arranged downstream thereof. In this way, the filters are designed such that each filter lets a different sub region of the audio frequency range through. In addition, an adjustable frequency-dependent network is embodied in each transmission channel behind the control amplifier. The individual transmission channels are combined on the output side and fed to a power amplifier, which finally controls the receiver.